Linux 4.1: No need for do_sync_read

Linux 4.1: No need for do_sync_read

Make the test here a bit more specific. do_sync_read no longer
exists, but we don't use it for new kernels.  Trying to define it
here in terms of generic_file_read is not helpful as that doesn't
exist anymore.

Change-Id: Iffb059716165436c3439e66db15002cdec5dfc16
Reviewed-on: http://gerrit.openafs.org/11848
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams <3chas3@gmail.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>